The exponential increase in the amount of data processing that is required by a client device, together with the continuously expanding availability of internet access to a growing number of client devices populated across multiple continents, introduces a technically complex and demanding challenge to an infrastructure handling a tremendous amount of data related to such data processing. Specifically, storage centers must be able to handle terabytes of data and a constituent interconnect network must transfer the terabytes of data among the storage centers or from individual storage centers to client devices at rates on order of terabits per second.
Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information. Fiber is preferred over electrical cabling when high bandwidth, long distance, or immunity to electromagnetic interference are required.
The development of single-channel and multi-channel optical fiber transceivers has facilitated ultrahigh data-rate communications. An optical fiber shows low insertion loss and, contrary to conventional electrical transmission lines, does not suffer from skin effect at high frequencies.
Skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is largest near the surface of the conductor, and decreases with greater depths in the conductor. The electric current flows mainly at the “skin” of the conductor, between the outer surface and a level called the skin depth. The skin effect causes the effective resistance of the conductor to increase at higher frequencies where the skin depth is smaller, thus reducing the effective cross-section of the conductor. The skin effect is due to opposing eddy currents induced by the changing magnetic field resulting from the alternating current.
A transimpedance amplifier (TIA) is a current-to-voltage converter, most often implemented using an operational amplifier. Appearing as the first stage of an optical receiver chain, a TIA is driven by a photodiode which converts optical power to electrical current. The TIA amplifies the electrical current to a proper voltage level required for a subsequent decision circuit to recover data and clock with minimum bit-error-rate (BER). The design of a TIA entails tight trade-offs between receiver bandwidth, gain, jitter, noise, power dissipation, and chip area.
High-speed 40 Gbps optical transceivers have been reported in J. Kim et al., “A 40-Gb/s Optical Transceiver Front-End in 45 nm SOI CMOS,” and C. Kromer et al., “A 40 Gb/s optical receiver in 80-nm CMOS for short-distance high-density interconnects,” [1, 2].
Additionally, 40 Gbps single-channel and 4×25 Gbps multi-channel TIAs have been reported in C. Li et al., “A Low-Power 26-GHz Transformer-Based Regulated Cascode SiGe BiCMOS Transimpedance Amplifier,” and T. Takemoto et al., “A 25 Gb/s×4-channel 74 mW/ch Transimpedance Amplifier in 65 nm CMOS,” [3, 4].
However, multi-channel wireline systems inherently suffer from crosstalk between adjacent channels. Such a signal integrity issue due to crosstalk is aggravated at higher data-rates, as a higher TX power is required to overcome increasingly higher channel impairments and to relax RX sensitivity requirements.
It is within the aforementioned context that a need for ultra-broadband TIA for optical fiber communications has arisen. Through applied effort, ingenuity, and innovation, many of these identified problems have been solved by developing solutions that are included in embodiments of the present disclosure, many examples of which are described in detail herein.